KR20010060194A - Determination of actual defect size in cathode sputter targets subjected to ultrasonic inspection - Google Patents

Abstract

PURPOSE: A method for determining actual defect size in cathode sputter targets is provided to measure the actual size of a defect by using ultrasonic waves, and obtain standards for disposal by detecting a defect especially in an aluminum or aluminum-alloy target. CONSTITUTION: A method for determining actual size of internal target defects by ultrasonic inspection is characterized in that the amplitude of signals generated by ultrasonic inspection is compared to metallurgical size measurements obtained through the use of optical microscopes or scanning electron microscopes or scanning election microscopes. From this comparison, a correlation factor is obtained to determine the accuracy of the ultrasonic measurements. For a particular sputter target material, defect sizes obtained by ultrasonic inspection is then multiplied by the correlation factor to determine the actual defect size for that defect. The use of actual defect sizes to determine defect sizes from ultrasonic inspection provides a more accurate determination of defect sizes and provides a reliable element for accepting or rejecting targets for critical circuit manufacturing operations.

Description

How to determine the actual defect size on a bipolar sputter target by ultrasonography

The present invention relates to a method for nondestructive testing of sputter targets for internal defects, and more particularly to a method for determining the actual inclusion size of a defect measured by ultrasound examination.

Anodic sputtering is a deposition method associated with ion bombardment of a target consisting of a material to be deposited on a substrate. The target forms part of the anode assembly in an evacuated chamber containing an inert gas such as argon. The electric field and gas supplied between the anode assembly and the cathode in the chamber are ionized by collisions with electrons emitted from the surface of the anode, forming a plasma between the target surface and the substrate. Gas cations are attracted to the cathode surface and are deposited as a thin film on a substrate or substrates that are placed on a support where material particles that fall off when ions collide with the target are held at or near the cathode potential across the enclosed space. .

Such deposition techniques have been widely applied in electronics for coating semiconductor silicon wafers using aluminum or aluminum alloys in the manufacture of integrated circuits. Fabrication of integrated circuits in high density integrated circuits, such as DRAM memories with capacities far greater than 4 MB, requires the deposition of thinner (about 1 μm) metal interconnect layers, which are then etched to produce very fine lines ( Widths less than 0.5 [mu] m should be formed to allow individual access to each memory location. Under these conditions, defects in the metallization layer having a size close to the width of the interconnect line can lead to defects in the material and disposal of the integrated circuit during the etching operation of the integrated circuit.

For the production of current and next generation ultra-large scale integrated circuits, such as DRAM memory of 16 MB or more, the fineness of etching is significantly emphasized, and the line width reaches several tens of microns, i.e. 0.2 to 0.5 [mu] m. Defects, such as inclusions from targets deposited on semiconductor substrates during anode sputtering, are a major cause of integrated circuit disposal, and each year these defects cause significant losses in the electronics industry worldwide.

In order to reduce the number of thin film coated substrates discarded due to etching defects due to inclusions or other defects in the sputter target, aluminum and aluminum alloy anode sputter targets are inspected nondestructively for these internal defects. Ultrasonic test methods are typically used for inspection, in which the target is immersed in a liquid and the material is scanned to check for defects. Typically, the defect size is determined by comparing the amplitude of the resulting signal with a signal from an artificial defect of known size that is formed by machining into a reference target blank. As described in US Pat. No. 5,887,481, an ultrasonic sensor or probe is a flat bottomed hole with a diameter of 0.1 mm formed by machining into a target composed of the same alloy with metal properties similar to those of the product to be tested. Measured for constructed artificial faults. The target to be tested is then immersed in the liquid and the amplitude of the ultrasonic echo obtained is compared with the amplitude of the artificial defect to determine the relative size of the defect. In addition, the number of echoes exceeding an amplitude corresponding to 0.1 mm of artificial defects can be calculated. By this method, it is possible to prevent the use of such targets which may have a negative effect on the sputtered film quality by discarding targets with too many defects per unit volume or defects of huge size.

The disadvantage of this method is that the maximum allowable defect size at the sputter target that must meet the current line width size is approximately 10 times smaller than the minimum artificial defect size that can be machined and formed into the reference target blank. Therefore, there will be a significant discrepancy between the size of the artificial defect compared to the size of the actual defect.

Therefore, there is a need to develop a method for determining the actual defect size at the anode sputtering target following an accurate and relatively easy to perform ultrasound examination.

It is therefore an object of the present invention to provide a method for determining the actual defect size at an anode sputter target by ultrasound examination.

Summary of the Invention

The present invention provides a method for nondestructively testing sputter targets by ultrasonic examination to determine the actual size of a defect in the target material. For this purpose, and in accordance with the principles of the present invention, ultrasonic signals generated from actual defects of unknown size were compared with metal size measurements of the same actual defects. For metal size determination, the actual defect can be determined by abrasion and wear of the surface of the target metal until the defect is exposed and measuring the size using an optical microscope or other measuring device. From the comparison of ultrasonic measurements and metal measurements, a correlation factor can be obtained for a particular target material that will give an accurate and reliable estimate of the actual defect sizes when multiplying the ultrasonic signals generated from the sputter target of the particular sputter target material. When the number of internal defects with a huge actual size exceeds the minimum allowable number, the sputter target can be discarded to avoid etching defects in the thin film coated substrate.

These and other objects and advantages of the present invention will become more apparent from the detailed description.

details

The sputter target was immersed in the liquid and internal defects were scanned using ultrasonic scanning equipment. The sputter target is typically placed on a fixture, which is lowered and immersed in the liquid. Ultrasound examination was performed by converging the ultrasound beam at a frequency of 5-50 MHz, advantageously 15-25 MHz, scanning across the thickness of the target. Defects in the material, such as inclusions, generate signals or wavelengths, and this information is sent to a computer, which plots the data. The amplitude of the ultrasound was measured and recorded.

The same test was then carried out by placing a portion of the target, such as in a plastic mold, and abrasion and wear of the target metal surface in small layers until one or more defects were exposed. This can be done using conventional wear and wear wheels using increasingly fine abrasive paper. If desired, conventional chemical etching can also be performed to further achieve exposure of the inclusions. The size of the defect was measured with the aid of a measuring device such as a scanning electron microscope (SEM) or an optical microscope, preferably an SEM of about 1000X-2000X magnification, which can accurately determine the microscopic defect size. Once the metal size measurement was obtained, it was compared with the amplitude of the signal generated from the ultrasound examination. Correlation factors can then be determined which, when multiplied by ultrasonic measurements, provide the actual size of the defect as measured by the metal test method. Once the correlation factor is determined for a particular sputter target material, another sputter target of that same material can be sonicated and the amplitudes of the signals generated thereby can be multiplied by the correlation factor to determine the actual defect size. Thus, once the correlation factor is determined, there is no need to run the metal test again to accurately determine the size of the defects in the sputter target material.

As an example, Al / 0.5% Cu sputter targets were inspected for inclusions and other defects using ultrasonic transmitters at frequencies in the range of about 15-25 MHz. Four defects were selected and the amplitude of the resulting signal showed an average defect size of 250 μm. This sputter target blank was then cut out and samples were taken from the defective part. These samples were first placed, worn and abraded and then microscopically examined using a SEM / EDAX (electron emission analyzer) at a magnification of 1000X-2000X and many defects were located. Photomicrographs were taken and the average size of the defects measured thereby was 25 μm. The correlation factor determined from these data was 0.1. In this way, for Al / 0.5% Cu sputter target materials, the actual defect size for each detected defect can be determined by multiplying the correlation factors of 0.1 by the amplitudes of the signals generated from the ultrasound examination.

The method of the present invention allows the defect size for sputter targets provided for ultrasound examination to be determined more accurately and descriptively than the previous methods. Because this method utilizes real defects rather than artificially formed defects using a machine, it is a better means of avoiding the disadvantages of the prior art methods associated with artificial defects and of accepting or discarding targets for critical circuit fabrication tasks. To limit the likelihood of defective sputter targets being sent to consumers. In addition, the method of the present invention saves the time and cost required for defect evaluation since each detected defect does not need to be compared with a reference target defect to determine its size.

Correlation factors vary from metal to metal and from alloy to alloy, so an initial correlation test should be performed on a particular type of sputter target material to determine the corresponding correlation factor for that particular material. For aluminum and aluminum alloys with low alloy content, the correlation factor was determined to be about 0.1. Once the correlation factor is determined, there is no need to run the correlation test again for this particular material. The principles of the present invention apply to any type of metal or alloy used for the production of sputter targets.

Once the actual bond sizes are determined for internal defects detected in the sputter target material, it can be determined to accept or discard this target. Typically, sputter targets are discarded when the number of internal defects with actual sizes greater than the predetermined maximum size exceeds the maximum allowable amount. In an embodiment of the present invention, at a current line width of 0.2-0.5 μm, the predetermined maximum defect size is about 50 μm, and the number of internal defects with actual sizes larger than the predetermined size results in a maximum allowable amount of 25 on a 12 inch diameter target. Should not be exceeded.

Although the invention is illustrated by the description of these embodiments, which are described in detail, this is not intended to limit or limit the scope of the claims. Additional advantages and modified methods will be readily apparent to those skilled in the art. Therefore, in its broader aspects, the invention is not limited to the specific details shown and described, representative apparatus and methods, and illustrative embodiments. Accordingly, applications from these details will be possible without departing from the spirit or scope of Applicants' general inventive concepts.

As mentioned above, the method of the present invention provides a method of determining the actual defect size at the anode sputter target by ultrasonic examination.

Claims (10)

A method for nondestructively determining the actual size of target defects provided for ultrasound examination, the method comprising the following steps: Scanning the material and recording the amplitude of the generated signal to obtain an ultrasonic measurement of the magnitude of the actual internal defect with an unknown size in the sputter target material; Exposing internal defects and measuring their actual size using a measuring device to obtain metal measurements of the size of the internal defects; And Correlating the ultrasonic measurements with the metal measurements to obtain a correlation factor for the sputter target material that will provide the actual size for this defect when multiplied by future ultrasonic measurements of internal defects. The method of claim 1, wherein metal measurements are obtained by abrasion and wear of one or more surface layers of the sputter target material until internal defects are exposed. The method of claim 1, wherein the metal measurements are obtained by exposing the defects using a scanning electron microscope and measuring the actual size. The method of claim 1, wherein the metal measurements are obtained by exposing the defect using an optical microscope and measuring the actual size. A method of removing a defect target having an unacceptable amount of internal defects larger than a predetermined size, the method comprising the following steps: Scanning the material and recording the amplitude of the generated signal to obtain an ultrasonic measurement of the magnitude of the actual internal defect with an unknown size in the sputter target material; Obtaining metal measurements of the size of the internal defects by exposing the internal defects and measuring their actual size using a measuring device; Correlating the ultrasonic measurements with the metal measurements to obtain a correlation factor for the sputter target material that will provide the actual size for this defect when multiplied by future ultrasonic measurements of internal defects; Obtaining ultrasonic measurements for each of one or more internal defects of unknown size in the sputter target comprised of the sputter target material; Multiplying ultrasonic measurements for each internal defect by a correlation factor to determine the actual size of each internal defect; And Discarding the sputter target in which the number of internal defects having an actual size larger than the predetermined size exceeds a minimum allowable amount. 6. The method of claim 5, wherein the metal measurements are obtained by abrasion and wear of one or more surface layers of the sputter target material until internal defects are exposed. 6. The method of claim 5, wherein the metal measurements are obtained by exposing the defect and measuring the actual size using a scanning electron microscope. 6. The method of claim 5, wherein the metal measurements are obtained by exposing the defect using an optical microscope and measuring the actual size. A method of removing a defective aluminum target having an unacceptable amount of internal defects greater than a predetermined size, the method comprising the following steps: Obtaining ultrasonic measurements for each of one or more internal defects of unknown size in the sputter target comprised of aluminum or aluminum alloy; Multiplying the ultrasonic measurements for each internal defect by a correlation factor of about 0.1 to determine the actual size of each internal defect; And Discarding the sputter target in which the number of internal defects having an actual size larger than the predetermined size exceeds a maximum allowable amount. 10. The method of claim 9, wherein the predetermined size is less than 50 μm and the maximum allowable amount is 25.